1. Field
Example embodiments relate to area tracking systems and methods of tracking electronic devices, and more particularly to an area tracking system including a distributed network of short range sensors and methods of detecting the location of electronic devices using the short range sensors.
2. Description of the Related Art
Short range wireless connectivity for exchanging data between electronic devices is widely used. For example, Bluetooth radios are resident in a wide range of electronic devices and in almost all mobile phones and smart phones. Bluetooth is an open wireless technology standard for exchanging data over a range from about 1 m to about 100 m using frequency-hopping spread spectrum which divides data over as many as 79 bands (1 MHz each) in the range 2402-2480 MHz.
A multitude of services may be offered to a user using a Bluetooth radio to connect a foreign electronic device to a user's device. Many of the services can expose private data or allow the foreign party to control the user's device. Accordingly, it is in the interest of the user to be able to screen which devices are allowed to connect to their device. However, for convenience, it is also in the interest of the user to allow foreign Bluetooth devices to automatically establish a connection without user intervention when they come into range.
To accommodate both interests, Bluetooth uses a process called pairing to establish a connection between electronic devices. A user generally initiates pairing manually by exposing their device's Bluetooth link to other devices. The pairing process is typically triggered automatically the first time a device receives a connection request from a device with which it is not yet paired. Once a pairing has been established each device retains a record of the pairing and the devices may subsequently reconnect to each other without user intervention.
Bluetooth is a packet-based protocol with a master-slave relationship. The master device is responsible for timing and access control in a Bluetooth network (e.g., a “piconet”) and may be connected to as many as 7 slave devices.
Each Bluetooth enabled device includes a Bluetooth radio that is identified by a unique permanent 48-bit Bluetooth Device Address (BD_ADDR). In general, electronic devices including Bluetooth radios are personal to a specific user and the detection of a specific BD_ADDR in most cases is the same as detection of the specific user. In certain cases, for example as with a security supervisor in an airport, the user carries multiple Bluetooth enabled devices and the detection of more the one of the devices increases the probability that the user is present.
The detectability of a Bluetooth device is dependent on a mode setting of the device. In a discovery/inquiry mode, a discovering device sends identification (ID) packets including an access code such as a General Inquiry Access code (GIAC), a Dedicated Inquiry Access Code (DIAC) or a Limited Inquiry Access Code to every device in proximity of the discovering device. Any device in the discoverable mode that is within range responds to the ID packets by sending a Frequency Hop Synchronization (FHS) packet that discloses the BD_ADDR and native clock (CLKN) of the discovered device.
However, many electronic devices in widespread usage are configured to be in a non-discoverable mode. For example, certain phones do not promiscuously respond to a general discovery inquiry due to security and privacy concerns. Allowing promiscuous discovery may result in the user being sent messages they are not intended to receive, thereby allowing phone spamming. The setting for discoverability is typically not exposed to a user and is often fixed by the manufacturer of the electronic device.
Electronic devices that are not in the discoverable mode but are set to be connectable can still be detected in the page and page scan states. In paging, the master device will transmit an ID packet including a Device Access Code (DAC) that is based on the Lower Address part (LAP) of the user's BD_ADDR. When the electronic device of the user detects the ID packet including the user device's DAC, it will reply by transmitting the user device's DAC back to the discovering device. A typical response time to paging is 1 sec or less. In complex and/or cluttered radio environments, a response time may be 2-3 seconds.
Although a user device is discoverable in the page and page scan states, the detecting device must have possession of, for example, the user's DAC.